The anomalous relaxivity of Mn3+ (TPPS4)

It was recently reported (C-W. Chen et al., FEBS Lett. 168, 70 (1984)) that water solutions of Mn3+ (TPPS4) have a surprisingly high relaxivity at 20 MHz and 37 degrees C, greater than most Mn2+ complexes including the hexaaquoion. Because Mn3+ (TPPS4) is highly stable, and porphyrins in general are tumor-seeking, we have sought to understand the origin of the large relaxivity by comparing the 1/T1 NMRD profiles (magnetic field dependence of 1/T1 of solvent protons) of Mn3+ (TPPS4) solutions with those of a number of other small Fe3+ and Mn2+ complexes. By relating the measured NMRD profiles to the theory of relaxation by magnetic dipolar interactions, in a form appropriate for small paramagnetic solute molecules, we establish that the theory affords an excellent quantitative description of the relaxation behavior of all the samples, and confirm that the relaxivity of Mn3+ (TPPS4) is anomalously high. The effect is attributed, in part, to the anisotropy of the ground-state wavefunction of Mn3+ in the porphyrin complex, effectively bringing the spin density of the Mn3+ ions closer to the protons of the coordinated water molecules than would a spherically symmetric S-state ion. In addition, the paramagnetic relaxation time of the Mn3+ spins, though short, is longer than would be anticipated for a non-S-state ion, and increases substantially with magnetic field above about 2 MHz. In this regard, Mn3+ (TPPS4) may be one of a class of molecules with properties particularly favorable for use as contrast-enhancing agents in magnetic resonance imaging.

Relaxation of water protons in the intra- and extracellular regions of blood containing Gd(DTPA)

The magnetic field dependence of the longitudinal relaxation rates 1/T1 (NMRD profiles) of blood and plasma from rabbits before and after injection of Gd(DTPA) are reported as a function of magnetic field strength from 0.01 to 50 MHz. Over 100 values along the time-dependent magnetization were recorded for each 1/T1 and analyzed for multiple exponentials. From these data, which indicate a single exponential, from the measured Gd content of each sample, and the NMRD profiles, we show that Gd is in the extracellular space only and is present as rotationally mobile Gd(DTPA), uncomplexed with protein or blood cells; and that the water protons exchange rapidly between the intra- and extracellular regions.

Magnetic field dependence (NMRD profile) of 1/T1 of rabbit kidney medulla and urine after intravenous injection of Gd(DTPA)

The measurement of NMRD profiles of water protons of excised tissues containing paramagnetic metal ions is one of the few ways of determining the biochemical and biophysical state of these ions in vivo. It is of critical importance, for example, to verify that Gd, injected as Gd(DTPA) to enhance contrast in MRI, remains chelated, since free Gd ions are highly toxic. We have investigated this in the renal medulla of rabbits. Fitting the magnetization data at each field of the dispersion to a single exponential shows that Gd accumulates predominantly in the renal medulla, from which it is cleared within 18 hours, and that Gd(DTPA) introduced intravenously into rabbits is excreted as Gd(DTPA) in the urine as rotationally mobile as in neat water. Taking a larger data set at each field and fitting it to the sum of two exponentials, since the errors of the single exponential analysis were larger than for other tissues, shows that the relaxation behavior of the renal medulla, free of contrast agent, can be well-described by a single relaxation rate at 37 degrees C. For increasing concentrations of Gd in the medulla, as determined by ICP analysis, two relaxation rates are required to account for the data, due to compartmentalization of tissue water and inhomogeneous distribution of Gd. These results, and similar data after mild mechanical disruption of renal structures, show unequivocally that the Gd in the renal medulla remains the chelate complex Gd(DTPA) and rotationally mobile, for dosages up to 300 mumoles/kg injected.

The human cellular abl gene product in the chronic myelogenous leukemia cell line K562 has an associated tyrosine protein kinase activity

Three antisera against the mouse v-abl gene product were used to identify two potential human c-abl gene products in the chronic myelogenous leukemia cell line K562. Two antipeptide sera were generated in rabbits using the predicted amino acid sequence of the mouse v-abl gene product. One antiserum was made against a polypeptide overlapping the in vivo tyrosine phosphorylation site of murine P120gag-abl and what is believed to be a homologous tyrosine phosphorylation site of the predicted normal human c-abl gene product (v-abl 263-280). The second antipeptide serum, abl 389-403, was generated against a predicted hydrophilic peptide of the v-abl gene product. Immunoprecipitation from K562 cells metabolically labeled with [32P]orthophosphate by a mouse tumor regressor and abl 389-403 antipeptide sera detected two proteins of 190,000 and 240,000 Da. Both proteins were labeled primarily at serine and, to a much lesser extent, at tyrosine residues. Immune complex kinase assays using conditions that allow the tyrosine phosphorylation of P120gag-abl showed that in vitro phosphorylation of P190 and P240 occurs primarily at tyrosine residues. The detection of these enzymatically active human c-abl gene products is a rare observation which may be in part attributed to the c-abl gene translocation from chromosomes 9 to 22 occurring in the vast majority of chronic myelogenous leukemia patients.